Pipelines used to transport products such as fuel, gas or hazardous liquids, particularly fuel pipelines, require periodic maintenance which involves cleaning their outer surfaces and providing them with protective coating, e.g., coating for protecting the outer surfaces of the pipes from corrosion. Since these pipelines may reach thousands of kilometers in length, the maintenance is effected in stages, viz. successively on sections thereof, which have a length in the order of tens of meters. Each section is subjected to maintenance at intervals of a few years, but in view of the great length and weight of the pipelines, especially when containing liquid, the overall maintenance operations are extremely cumbersome and costly.
A great deal of damage to a pipeline is caused by external corrosion, and the maintenance procedures referred to in the present application relate to the removal of external corrosion and of a pipeline protective layer, which is well known to those skilled in the art, and the subsequent rehabilitation of the pipeline, such as by applying an anti-corrosion coating.
Prior art corrosion and protective layer removal devices generally include a spray unit, which rotates completely around the pipeline section, for sandblasting its external periphery. The spray unit comprises at least nozzle, from which sand is discharged by means of high pressure air or water. Alternatively, the spray unit may be hand held or be automatically operated by a mechanism having up to six degrees of freedom. In order to allow the spray unit to spray the entire periphery of a pipeline section, the buried section needs to be exposed and raised to a considerable height, while being securely supported. Such maintenance procedures may be carried out as fuel or gas is still within the pipeline, for more efficient delivery of the fuel or gas, thereby increasing the weight and complexity of the pipeline raising.
It is an object of the present invention to provide a method and apparatus for pipeline maintenance by which the entire periphery of a pipeline section is sprayed with suitable material.
It is an additional object of the present invention to provide a method and apparatus for pipeline maintenance which reduces, with respect to the prior art, the height to which a pipeline section needs to be raised, thereby reducing the risk for mechanical failure.
It is an additional object of the present invention to provide an apparatus for pipeline maintenance that is axially displaceable along the length of the pipeline.
It is yet an additional object of the present invention to provide a method and apparatus for pipeline maintenance which is cost effective.
Other objects and advantages of the invention will become apparent as the description proceeds.